Two tips for using the profile manager: I recommend using the default profile folder location suggested by the dialog, and not deleting any profiles without making backups first.

Can you download the PDFs under either of those scenarios?

Two common troubleshooting techniques that I think have not yet been mentioned are: Firefox safe mode and a new Firefox profile.
* Safe mode bypasses your extensions, certain customizations, and some performance features that can create issues (but probably not these issues).
* A new profile looks like a new install of Firefox, and has fresh databases and a clean cache, but it should have most or all of the plugins installed on your system.
Here are the procedures if you want to try:
(1) Safe Mode
You can restart Firefox in Safe Mode using
Help > Restart with Add-ons Disabled
In the dialog, click "Start in Safe Mode" (''not'' Reset)
More info: [[Troubleshoot Firefox issues using Safe Mode]].
(2) New Profile
Refer to this article for how to start Firefox (all windows need to be closed first) in the Profile Manager: [[Use the Profile Manager to create and remove Firefox profiles]]. Any time you want to switch profiles, close Firefox and return to this dialog.
Two tips for using the profile manager: I recommend using the default profile folder location suggested by the dialog, and not deleting any profiles without making backups first.
Can you download the PDFs under either of those scenarios?

Question owner

I have created a new profile. Thanks for sharing that. Now it gets more interesting. When I go to the website and click on the link to enter the passwords I get "invalid security certificate." I have deleted the cert8.db file but that doesn't help. So now I don't know if I can just ignore that security message and continue? I can't risk it being insecure as it is a financial site. Any thoughts. This is so crazy, I've never encountered so many issues with a browser.

I have created a new profile. Thanks for sharing that. Now it gets more interesting. When I go to the website and click on the link to enter the passwords I get "invalid security certificate." I have deleted the cert8.db file but that doesn't help. So now I don't know if I can just ignore that security message and continue? I can't risk it being insecure as it is a financial site. Any thoughts. This is so crazy, I've never encountered so many issues with a browser.

If you view the "technical details" for the certificate problem, what do you find?

Some security software or services may proxy your connection, and when you are accessing a secure site, this may not work correctly. Or should I say, Firefox may detect the proxy and throw up an error. Such proxying may be done by an add-on, or may be implemented through the connection setting:

Firefox menu > Preferences > Advanced > Network > "Settings" button

If you view the "technical details" for the certificate problem, what do you find?
Some security software or services may proxy your connection, and when you are accessing a secure site, this may not work correctly. Or should I say, Firefox may detect the proxy and throw up an error. Such proxying may be done by an add-on, or may be implemented through the connection setting:
Firefox menu > Preferences > Advanced > Network > "Settings" button

Question owner

Currently selected is use system proxy settings. Are you suggesting this should be changed or just over ride the security warning and mark the site as a trusted one?

Technical details
Invalid security certificate
no issuer chain
sec_error_unknown_issuer
Currently selected is use system proxy settings. Are you suggesting this should be changed or just over ride the security warning and mark the site as a trusted one?

Helpful Reply

Sounds that this is a case of a missing intermediate certificate.

Check out why the site is untrusted (click "Technical Details to expand that section) and if this is caused by a missing intermediate certificate then see if you can install this intermediate certificate from another source.

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

Click the link at the bottom of the error page: "I Understand the Risks"

Click the "View..." button and inspect the certificate and check who is the issuer.

You can see more Details like intermediate certificates that are used in the Details pane.

Sounds that this is a case of a missing intermediate certificate.
Check out why the site is untrusted (click "Technical Details to expand that section) and if this is caused by a missing intermediate certificate then see if you can install this intermediate certificate from another source.
You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.
*Click the link at the bottom of the error page: "I Understand the Risks"
Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".
*Click the "View..." button and inspect the certificate and check who is the issuer.
You can see more Details like intermediate certificates that are used in the Details pane.

Question owner

It appears that creating a new profile and then adding the site as an exception to get the certificate worked!

I wish I could understand why I needed to create a new profile and why when I did I had to add the site as an exception to get the certificate.

Hopefully whatever caused this won't happen again. Thank you to everyone who assisted me with all their suggestions. It was a great help and massively appreciated.

In this day and age I found it remarkable that the site I was trying to pull pdf's from had a "tech help" department where no one understood the mac platform and were incapable of offering any assistance.

It appears that creating a new profile and then adding the site as an exception to get the certificate worked!
I wish I could understand why I needed to create a new profile and why when I did I had to add the site as an exception to get the certificate.
Hopefully whatever caused this won't happen again. Thank you to everyone who assisted me with all their suggestions. It was a great help and massively appreciated.
In this day and age I found it remarkable that the site I was trying to pull pdf's from had a "tech help" department where no one understood the mac platform and were incapable of offering any assistance.